With the aging of the population, dementia patients have continued to increase, which has become a significant social issue in Japan. Mild cognitive impairment (MCI) is a stage before dementia, and the number of elderly people who have MCI is presumably quite large.
MCI is a symptom at the intermediate stage (gray area) between dementia and the healthy state of a person. MCI is a state in which one of the cognitive functions (memory, determination, reasoning, execution, etc.) has a problem, but daily activities can be performed without any difficulty. When left untreated, MCI continues to reduce cognitive functions, and about half of all MCI patients are considered to progress to the stage of dementia. Since there is so far basically no cure for dementia, it is highly important to take appropriate action at the MCI stage to prevent the progression of symptoms.
There are mainly four types of dementia: Alzheimer's dementia, Lewy body dementia, vascular dementia, and frontotemporal dementia.
Of these, Alzheimer's disease is the most common dementia and accounts for more than half of all cases of senile dementia. Alzheimer's disease is characterized by progressive dementia occurring from the presenile stage to the senile stage, and the number of patients in Japan nowadays is thought to be 3 million or more. Clinical symptoms of Alzheimer's disease include memory impairment, higher-brain dysfunction (e.g., apraxia, agnosia, aphasia, and constructional apraxia), etc. The deposition of amyloid β protein and tau protein in the brain causes neuron death, which is thought to be the cause of Alzheimer's disease.
Four anti-dementia medications (donepezil, memantine, galantamine, and rivastigmine) are currently used to treat dementia. It is generally thought that administration of one or two medications among the four medications can delay the progression of dementia.
In order for the brain to function smoothly, sufficient ATP (adenosine triphosphate) is required as an energy source, but most dementia patients have reduced ATP production. ATP production decreases every year after age 40, and ATP production at age 80 is said to be about 60, based on 100 at age 40. A reduction in ATP level accelerates the decline in cognitive functions (specifically, dementia is more likely to develop), but the four anti-dementia medications cannot increase the ATP level although they increase acetylcholine in the brain. Moreover, although a cerebral circulation metabolism improvement agent can be used to promote ATP production, it can be used only after organic dysfunction, such as cerebral infarction, under the current system.
Patent Literature 1 has reported that there is a possibility of using a Ginkgo biloba extract, combined with phosphatidylserine, as an active ingredient of a food or drug for improving dementia and Alzheimer's disease. On the other hand, some documents have reported that supplements containing vitamin B, vitamin C, vitamin E, β-carotene, folic acid, etc., either singly or in a combination of 2 or 3 or so, are not effective for improving cognitive functions (Non-patent literature 1 to 5).